Transistorized ignition system utilizing a magnetically actuated reed switch



March 1967 R. c. MLAUGHLIN 3,308,341

TRANSISTORIZED IGNITION SYSTEM UTILIZING A MAGNETICALLY ACTUATED REED SWITCH Filed Feb. 10, 1964 INVENTOR.

Robert C. McLaughlin BY W MGL Q United States Patent 3,308,341 TRANSISTORIZED IGNITION SYSTEM UTI- LIZING A MAGNETICALLY ACTUATED REED SWITCH Robert C. McLaughlin, Bloomingdale, Ill., assignor to Motorola, Inc., Franklin Park, 11]., a corporation of Illinois Filed Feb. 10, 1964, Ser. No. 343,652 2 Claims. (Cl. 315219) This invention relates to ignition systems for internal combustion engines, and more particularly to an improved transistorized ignition system utilizing a magnetically :actuated reed switch.

Ignition systems for internal combustion engines generally utilize some type of switching circuit in series with an igniton coil for supplying and cutting off current through the coil. Cut off of current in the ignition coil causes a collapsing field which induces a high voltage pulse in the coil secondary. This pulse is supplied by a distributor to the internal combustion engine for firing the fuel mixture in a combustion chamber.

In their simplest form, such switching circuits generally include a pair of cam actuated mechanical breaker points operable in timed relation with the internal combustion engine. The breaker points are connected in series with the ignition coil across a source of potential. The high current carried by these breaker points, and the corrosion and piting thereof, necessitates frequent replacement and contributes to a certain amount of unreliability.

In order to avoid the above problem, ignition systems have been proposed utilizing transistors for interrupting the main current through the ignition coil. Such ignition systems have the advantage that the coil current is switched electronically rather than through the breaker points. Control circuits are required for the transistors to cause conduction and non-conduction thereof in timed relation to the engine. Various means have been utilized to synchronize the operation of the control circuit for the transistors with the internal combustion engine. Such systems, however, have been complex in their assembly and operation, and certain of such systems have exhibited instability with temperature or voltage variation. To :avoid the need for very high amplification in the control circuit, such systems have in some causes incorporated the conventional mechanical breaker points in the control circuit. The latter system has the disadvantage of mechanical wear and susceptibility to faulty operation due to contamination by forign particles. Conventional mechanical breaker points also present insulation problems in positive .ground systems due to inherent characteristics of their mechanical construction.

It is therefore an object of this invention to provide a stable improved ignition system for an internal combustion engine which is highly reliable and simple of construction.

Still another object of the invention is to provide a low cost transistorized ignition system utilizing improved means for controlling the transistors thereof.

Another object of the invention is to provide an ignition system for an internal combustion engine which is readily incorporated in existing positive or negative ground systems utilizing distributors of standard construction.

It is another object of the invention to provide an ignition system for an internal combustion engine wherein mechanical wear and the possibility of contamination of switch contacts by foreign particles is substantially reduced.

A feature of the invention is the provision of an ignition system for an internal combustion engine utilizing a 3,308,341 Patented Mar. 7, 1967 magnetically operable reed switch in a control circuit for semiconductor switch devices to operate the same between conducting and non-conducting states.

Another feature of the invention is the provision of a magnetically actuated reed switch for synchronizing a control circuit with the engine which switch is placed adjacent an annular magnet in a distributor, which annular magnet has alternate polarity portions about the periphery thereof.

A further feature of the invention is the provision of a transistorized ignition system utilizing a switching transistor or transistors in series with the ignition coil for interrupting the current therein, and the further provision of a control circuit for the switching transistor or transistors which control circuit includes a further transistor the conduction of which is determined by a magnetically actuated reed switch.

In the drawing:

FIG. 1 is a schematic illustration of the ignition system of the invention;

FIG. 2 illustrates an alternate circuit configuration which can be used in the system of FIG. 1; and

FIG. 3 is a cross sectional view of a distributor structure which can be used in the system of FIG. 1.

In accordance with the invention, an ignition system for an internal combustion engine includes an ignition coil and a switching transistor connected in series therewith across a source of potential for interrupting the current through the coil to produce firing pulses therein. A control circuit, including a control transistor, is provided for the switching transistor. The conduction of the control transistor is determined by a magnetically actuable encapsulated reed switch which is placed adjacent a rotating magnetic structure in a distributor. The rotating magnetic structure opens and closes the reed switch in synchronism with the internal combustion engine to provide properly timed firing pulses.

One embodiment of the invention includes a pair of switching transistors connected in series with the ignition coil, and a control transistor connected to the bias circuit for the two transistors to control the bias circuit. The magnetic reed switch is connected to the base portion of the controlling transistor to switch that transistor on and off thereby switching the bias for the first two transistors to cause interruption of coil current. The rotating magnetic structure which actuates the reed switch may be an annular magnet with alternate poles of opposite polarity regularly spaced about the periphery thereof. The magnet may be rotated by the distributor rotor shaft whereby the poles alternately align themselves with respective reeds in the reed switch to cause the switch to open and close.

Referring now more particularly to FIG. 1, there is shown an ignition system for an internal combustion engine 11. Engine 11 has a plurality of spark plugs 12 for igniting the fuel mixture in the cylinders of engine 11. High voltage firing pulses are supplied to spark plugs 12 by a distributor 13 which has a plurality of fixed contacts 14 connected to respective ones of spark plugs 12, and a moving contact 15 connected across the secondary winding of a high voltage ignition coil 16.

As shown in FIG. 1, ignition coil 16 is of the well known auto-transformer type. However, the double winding type of transformer may also be used within the scope of the invention. When current flowing through the primary of ignition coil 16 is suddenly interrupted, a high voltage spike will be induced in the secondary thereof. It is this spike that is applied to moving contact 15 of distributor 13 and from there to one of the spark plugs 12 of internal combustion engine 11. The primary of ignition coil 16 is connected to the source of current, namely storage battery 17, by a pair of transistors 18 and 19. Battery 17 may be charged by an alternator or generator 21, the output of which may be regulated by regulator 23 in a well known manner. Also connected in series with the primary of coil 16 and transistors 18 and 19, are ignition switch 25 and ballast resistor 27.

As previously stated, transistors 18 and 19 control the conduction of current to the primary of ignition coil 16. Upon interruption of current in coil 16, a high reverse voltage occurs. Zener diodes 28 and 29 are connected across the emitter and collector portions of transistors 18 and 19 respectively to prevent the reverse voltage across the emitter and collector portions of the transistors from exceeding their breakdown voltage. A resistor 31 is connected across the emitter and base portions .of transistor 18, and the base portion of transistor 18 is connected through an isolating diode 33 to resistor 35. Resistor 37 connects the base portion of transistor 19 to its emitter portion, and the base portion is also connected to resistor 36. A control transistor 41 has its emitter portion connected to the junction between resistors 36 and 35, and has its collector portion grounded.

Upon conduction of transistor 41, transistor 19 will be forward biased through resistor 36, whereas transistor 18 will be forward biased through resistor 35 and diode 33. This will cause current to flow in coil 16. When transistor 41 is cut off, the potential on the base portions of both transistors 19 and 18 will rise quickly toward their respective emitter potentials due to resistors 37 and 31, cutting these transistors off. This interrupts current through coil 16 producing a firing pulse therein.

The conduction of control transistor 41 is, in turn, controlled by a circuit responsive to the speed and timing of engine 11. A resistor 43 connects the base portion of transistor 41 to battery 17 through ignition switch 25. The base portion of transistor 41 is also connected to ground through a magnetically actuable reed switch 45.

Reed switch 45 comprises a pair of reeds 47 and 48 which are normally open. Reed switch 45 is glass encapsulated and placed adjacent a rotating magnet 50 which, during the course of its rotation, will align poles of opposite polarity adjacent respective ones of reeds 47 and 48. This causes the reeds to attract one another and therefore to close. The alternate poles marked N, S, N, etc. around the periphery of the annular magnet are uniformly spaced to operate the reed switch at regular annular positions of the magnet. As the magnet 50 continues rotation, the alternate poles produce fields which are in opposite directions to open the reeds at the half way point and then close them again once the field is completely reversed. It should be noted that the poles at the half way point may actually force the reeds apart in the event that they tend to stick together due to magnetic retentivity or moisture.

With switch 45 closed, the base portion of transistor 41 will be grounded and hence transistor 41 will be driven into conduction to ground the juncture between resistors 36 and 35. When reed switch 45 opens, the base portion of transistor 41, which is connected to battery 17 through resistor 43, will rise to battery potential, actually reverse biasing the transistor 41 to insure rapid cut off.

Magnetically actuable reed switches, of the general nature of switch 45, are commercially available from numerous sources, one such source being Hamlin Inc. of Lake Mills, Wisconsin, under the designation MRG-l. The glass encapsulating tube may be approximately 4;" in diameter and less than 1 long. The reed may be a nickel iron alloy and rhodium plated. As an alternative, the reeds may be gold diffused and/or nickel plated. Numerous other types of reed switches are available, and reed switches which are normally closed rather than open may also be obtained commercially. Because insulated connection is easily made to both ends of the reed switch it may be readily incorporated in positive or negative ground systems.

Referring to FIG. 2, an alternative circuit is shown. Only a single switching transistor 51 is used having a protective Zener diode 52. The base portion of transistor 51 is connected through resistor 57 to the emitter portion of a control transistor 61. Transistor 61, when conductive, will therefore cause resistor 57 to forward bias transistor 51 into conduction. Conduction of transistor 61 is controlled by a resistor 63 connecting the base portion of transistor 61 to the ignition switch, and by magnetically actuable reed switch 45. Closure of reeds 47 and 48 of switch 45 will forward bias transistor 61 into conduction and cause current flow through resistor 57. This forward biases transistor 51 into conduction. Upon opening of switch 45 the base portion of transistor 61 will rise to a cut off potential. This will allow resistive choke 55, which is connected across the emitter and base portions of transistor 51, to reverse bias transistor 51, cutting it off. This interrupts current through coil 16 and produces a firing pulse.

The physical placement of the magnetically actuated reed switch 45 in relation to the rotating magnet and other elements of the system may affect the operation of the system. In FIG. 3, a particular way of mounting the reed switch in a conventional distributor is shown. The distributor includes a housing 71 and a cap 72. A distributor shaft 73 extends upwardly into the housing and drives a drive plate 75. Drive plate 75 is connected through the usual spring biased fly weights 77 and drive pins 78 to a centrifugal advance plate 79.

Advance plate 79, drives the rotor shaft 81 upon which rotor 83 is mounted. Rotor 83 carries the moving contact 15 of the distributor, and the fixed contacts 14 of the distributor extend downwardly in the interior of cap 72. Rotor shaft 81 carries a cam 85, which may be the conventional type used to operate mechanical breaker points. A grommet 87 of rubber, plastic, or other suitable material is fitted over cam to be driven thereby and carries an annular magnet 89. Magnet 89 may be of powdered barium ferrite and is magnetized about the periphery thereof in alternate evenly spaced poles. The magnet need not be annular, however, and may be constructed without alternate poles. Instead of a rotating magnet, a fixed magnet with a rotating piece of soft iron might suffice.

Magnetic reed switch 45 is placed adjacent the periphery of magnet 89 and is carried in a channel formed in a phenolic support member 91. A further groove is provided in support member 91 for carrying the electrical leads 93 from switch 45. Support member 91 is secured to the vacuum advance cup 95 of the distributor in the same manner that the conventional breaker points are secured thereto. It may be desirable to provide a pole piece for each reed of switch 45 to help concentrate flux therein. The spacing of reed switch 45 from magnet 50 will alfect the dwell or conduction period. Also, the configuration of magnet 50 may be altered to affect dwell.

FIG. 3 is shown as a representation of how a rugged construction for the ignition system of the invention may be accomplished. The grooves in support member 91 may be filled with an insulating resin to insure against damage. By utilizing grommet 87 fitted over the conventional distributor cam, a distributor utilizing a conventional breaker cam and points may be readily adapted to the present ignition system merely by removing the points and adding the grommet, magnet, and reed switch. Other magnetic structures for actuating reed switch 45 are possible within the scope of the present invention.

It may therefore be seen that the invention provides an improved transistorized ignition system which is low in cost, simple of construction, and reliable in operation. The system utilizes a magnetic reed switch for triggering the control circuit for the transistor ignition, and is readily adaptable to existing conventional type ignition systems. Furthermore, the ignition system of the invention, although shown for negative ground polarity, will operate with positive ground polarity without modification of the circuit.

I claim:

1. In an ignition system having an ignition coil for providing firing pulses for an internal combustion engine, apparatus for interrupting current through the coil to produce firing pulses therein including in combination, transistor switching means having input, output and control portions, means adapted to connect said input and output portions of said transistor switching means in series with at least a portion of the ignition coil across a source of potential, and a control circuit connected to said control portion of said transistor switching means for controlling the conduction thereof, said control circuit including an encapsulated magnetic reed switch and a disc-like annular rotary magnetic member for operating said magnetic switch, means coupling said magnetic member to the internal combustion engine for rotating said member in synchronism with the engine, said magnetic member having north and south poles alternately positioned at regular intervals on the periphery thereof, said magnetic reed switch having two magnetic reed members adapted to engage each other to close circuit means through said reed switch, said reed members being positioned adjacent the periphery of said annular magnetic member, tangent thereto and in the same plane therewith, so that during rotation of said annular magnetic member opposite magnetic poles thereof are aligned with said reed members and polarize the same to opposite polarities so that said reed members attract each other and engage to close the circuit therethrough, and then like magnetic poles of said magnetic members are aligned with said reed members and polarize said reed members to the same polarity so that said reed members repel each other and separate to open the circuit therethrough, said magnetic reed switch alternately closing and opening said circuit means therethrough as said magnetic member rotates, said circuit means operating to alternately change the conduction of said control circuit means, said control circuit means causing intermittent operation of said transistor switching means to interrupt current in said ignition coil and producing firing pulses.

2. The structure of claim 1 further including a distributor housing and a distributor shaft extending therein and coupled to the internal combustion engine, a vacuum operated advance plate within said housing and including rn-eans supporting said encapsulated magnetic reed switch, and wherein said means coupling said rotary magnetic member to the internal combustion engine includes centrifugal advance means within said housing connecting said distributor shaft to said rotary magnetic member.

References Cited by the Examiner UNITED STATES PATENTS 2,112,214 3/1938 Tognola 123148 2,929,896 3/ 1960 Ronning ZOO-87 3,073,879 1/1963 Straub 3l5209 3,133,173 5/1964 Vriens 315209 3,250,955 5/1966 Krikac 315209 X OTHER REFERENCES Mayfield, M. R., High Performance Transistor Ignition System, appearing in Electronics World, June 1963, pp. 30, 31 and 62. Copy in Group 250.

References Cited by the Applicant UNITED STATES PATENTS 2,781,412 2/1957 Mike. 3,087,030 4/1963 Shebanow.

JOHN W. HUCKERT, Primary Examiner. D. O. KRAFT, Assistant Examiner. 

1. IN AN IGNITION SYSTEM HAVING AN IGNITION COIL FOR PROVIDING FIRING PULSES FOR AN INTERNAL COMBUSTION ENGINE, APPARATUS FOR INTERRUPTING CURRENT THROUGH THE COIL TO PRODUCE FIRING PULSES THEREIN INCLUDING IN COMBINATION, TRANSISTOR SWITCHING MEANS HAVING INPUT, OUTPUT AND CONTROL PORTIONS, MEANS ADAPTED TO CONNECT SAID INPUT AND OUTPUT PORTIONS OF SAID TRANSISTOR SWITCHING MEANS IN SERIES WITH AT LEAST A PORTION OF THE IGNITION COIL ACROSS A SOURCE OF POTENTIAL, AND A CONTROL CIRCUIT CONNECTED TO SAID CONTROL PORTION OF SAID TRANSISTOR SWITCHING MEANS FOR CONTROLLING THE CONDUCTION THEREOF, SAID CONTROL CIRCUIT INCLUDING AN ENCAPSULATED MAGNETIC REED SWITCH AND A DISC-LIKE ANNULAR ROTARY MAGNETIC MEMBER FOR OPERATING SAID MAGNETIC SWITCH, MEANS COUPLING SAID MAGNETIC MEMBER TO THE INTERNAL COMBUSTION ENGINE FOR ROTATING SAID MEMBER IN SYNCHRONISM WITH THE ENGINE, SAID MAGNETIC MEMBER HAVING NORTH AND SOUTH POLES ALTERNATELY POSITIONED AT REGULAR INTERVALS ON THE PERIPHERY THEREOF, SAID MAGNETIC REED SWITCH HAVING TWO MAGNETIC REED MEMBERS ADAPTED TO ENGAGE EACH OTHER TO CLOSE CIRCUIT MEANS THROUGH SAID REED SWITCH, SAID REED MEMBERS BEING POSITIONED ADJACENT THE PERIPHERY OF SAID ANNULAR MAGNETIC MEMBER, TANGENT THERETO AND IN THE SAME PLANE THEREWITH, SO THAT DURING ROTATION OF SAID ANNULAR MAGNETIC MEMBER OPPOSITE MAGNETIC POLES THEREOF ARE ALIGNED WITH SAID REED MEMBERS AND POLARIZE THE SAME TO OPPOSITE POLARITIES SO THAT SAID REED MEMBERS ATTRACT EACH OTHER AND ENGAGE TO CLOSE THE CIRCUIT THERETHROUGH, AND THEN LIKE MAGNETIC POLES OF SAID MAGNETIC MEMBERS ARE ALIGNED WITH SAID REED MEMBERS AND POLARIZE SAID REED MEMBERS TO THE SAME POLARITY SO THAT SAID REED MEMBERS REPEL EACH OTHER AND SEPARATE TO OPEN THE CIRCUIT THERETHROUGH, SAID MAGNETIC REED SWITCH ALTERNATELY CLOSING AND OPENING SAID CIRCUIT MEANS THERETHROUGH AS SAID MAGNETIC MEMBER ROTATES, SAID CIRCUIT MEANS OPERATING TO ALTERNATELY CHANGE THE CONDUCTION OF SAID CONTROL CIRCUIT MEANS, SAID CONTROL CIRCUIT MEANS CAUSING INTERMITTENT OPERATION OF SAID TRANSISTOR SWITCHING MEANS TO INTERRUPT CURRENT IN SAID IGNITION COIL AND PRODUCING FIRING PULSES. 